This invention pertains to a plasma reformer for dissociating H2O and hydrocarbon fuels to produce hydrogen for direct use or for use in a fuel cell and carbon oxides. More particularly it pertains to dissociating H2O into hydrogen and oxygen in a plasma reformer that uses a hydrocarbon fuel as an initiator and an intense electron field under non-equilibrium thermal plasma conditions to dissociate H2O.
Hydrogen powered fuel cells have long been recognized as having great potential for stationary power generation and for transportation applications. Advantages of fuel cells include their ability to generate power more efficiently than internal combustion engines and other conventional power sources while producing essentially no pollutants. However, currently, no scalable, cost-effective, environmentally attractive hydrogen production process is available for commercialization. Hydrogen can be produced from dissociation of H2O or from reforming of hydrogen fuels. Dissociation of H2O is ideal from an environmental perspective because it produces no greenhouse gases; however, dissociation of H2O through electrolysis is energy-intensive and prohibitively expensive.
Hydrogen can be produced from hydrocarbon fuels with use of conventional technologies such as steam reforming, partial oxidation, and auto-thermal reforming. For example, Takahashi in U.S. Pat. No. 5,746,985 and Edlund, et al in U.S. Pat. No. 6,221,117 teach use of steam reforming reactions; Krumpelts, et al in U.S. Pat. No. 5,942,346 and Ahmed, et al in U.S. Pat. Nos. 5,939,025 teach use of partial oxidation reactions. However, these technologies tend to require large components and to be not efficient in meeting large demands, a disadvantage for space-limited facilities such as fueling stations. There are also several technical issues such as capability for fast starts, fast response to load changes, sulfur contamination, and soot or carbon formation. One problem common to conventional reforming is sulfur removal. Conventional reformer technology requires removal of sulfur from liquid fuels, which is usually accomplished with use of catalysts and heavy heaters. Such components usually raise gas poisoning and temperature sensitivity issues. Also in conventional reformer technology, poor fuel dispersion will create uneven fuel distribution and result in carbon/coke formation in fuel-rich zones and hot spots in fuel-lean zones.
The inventor has developed technology for dissociating compounds in a thermoelectric reactor using ultra-pyrolysis techniques with thermal radiation enhancement, non-equilibrium reactions derived from electromagnetic forces, and energy trapping to achieve and maintain temperatures sufficient to achieve very high conversion rates. When the compound contains hydrogen, such as hydrocarbon fuels and hydrogen sulfide, its dissociation produces hydrogen. The inventor has taught the use of thermoelectric reactors to destroy volatile organic compounds in U.S. Pat. No. 5,614,156, to dissociate hydrogen sulfide into hydrogen and sulfur in U.S. Pat. No. 5,843,395, and to reform hydrocarbon fuels to produce hydrogen in U.S. application Ser. No. 10/121,390 now abandoned.
Such a reactor has recently been tested for reforming several transportation fuels to produce hydrogen. The results are given in Table 1.
TABLE 1FuelH2ElectricityConv.ConvEnergyConsumptiona,Eff.b,Eff.c,Eff.d,H2 Conc.eFuel%%%%(dry) %Methanol<3~10093–95~10064Ethanol<6~10094~10054Gasoline<6~10097~10065Note:aElectricity Consumption = (electrical power input)/(electrical power input + LHV of input fuel)bFuel Conversion Efficiency = 1 − (fuel in reformate)/(input fuel)cH2 Conversion Efficiency = (H2 measured in reformate)/(H2 theoretical value in equilibrium)dEnergy Efficiency = (LHV of H2 in reformate)/(LHV of input fuel + electric power input)eMeasured H2 concentration in reformate as dry basis. This concentration was measured right after the H2 reformer (without any other gas conditioning).LHV = Low Heating Value
The U.S. Department of Energy (USDOE), (Hydrogen Production and Delivery Research Solicitation No. DE-PS36-03GO93007, Jul. 24, 24, 2003, pares 2. c-7)1 estimates that currently it costs between $5.00 and $6.00 to produce a kilogram of hydrogen, and that this cost should be reduced to $1.50/kg to be competitive with conventional fuels. The USDOE has also set a primary energy efficiency of 75% to be met in the year 2010. The primary energy efficiency of conventional reformer technology for producing hydrogen currently ranges up to 70%. Thus a three to four-fold decrease in cost is necessary for hydrogen to become a competitively priced fuel. A significant fraction of the cost of hydrogen production is the cost of the hydrocarbon fuels that are reformed. If H2O were to replace hydrocarbon fuels as the primary source of hydrogen in a reformer, such cost reductions are feasible.
It is difficult to dissociate H2O with thermal energy because very high temperatures, in excess of 2500° C., are needed. Also, it is difficult to ionize H2O because it has a higher ionization energy potential and enthalpy formations of ions (12.6 eV and 976 kJ/mol, respectively) than hydrocarbon fuels of interest. For example, gasoline has an ionization energy of 9.8 eV and an enthalpy formation of ions of 737 kJ/mol. In addition, it is difficult to ionize H2O using high energy (“hard”) electrons because H2O is a small molecule that has a small bombardment target area for ionization by high energy (hard) electrons that are newly emitted from electrodes. However, H2O much more readily absorbs low energy (“soft”) electrons that have lost much of their energy in collisions with other ions and hydrocarbon molecules. Thus hydrogen can be produced in a reformer from dissociation of H2O through ionization and from dissociation of hydrocarbon fuels through heat and ionization when the temperature in the reaction chamber of reformer is sufficiently high (in excess of 700° C.) and when there is an intense field of low energy electrons. These conditions can be created or found in some plasmas.